Angiography apparatuses or systems are used for interventions in the heart in order, by means of X-ray imaging, to monitor these interventions. Angiography apparatuses of this kind typically have a C-shaped arm, on one end of which an X-ray source and on the other end of which an associated X-ray detector is mounted. The C-arm is freely pivotable about a patient couch and allows by this means the recording of two-dimensional real-time X-ray images (fluoroscopic recordings) of the patient from a wide variety of viewing angles.
Traditionally, angiography systems generate simple projected X-ray images on which structures such as heart shadows, guide wires, catheters and contrast-agent-filled catheters can be recognized. For some years, angiography systems have, through rotation of the C-arm around the patient, also been able to generate CT-like 3D images, on which soft tissue can be viewed three-dimensionally. The representation options are, however, restricted to the morphology, i.e. the structure, of the regions examined.
This invention deals with the problem of determining by means of angiography systems information about perfusion of the cardiac muscle. This problem is of special interest because a suitable method can, in contrast to the established methods for perfusion measurement (MR, SPECT, PET), be applied during an intervention.
Tissue perfusion or perfusion can be determined with a multiplicity of radiological methods such as e.g. magnetic resonance tomography (MR), computed tomography (CT), ultrasound or positron emission tomography (PET). Most of the methods are based on a contrast-agent bolus being injected and the concentration of the contrast agent being examined as a function of time.
A prerequisite for this is rapid image recording so as to be able to trace the passage of the bolus. The recording of images at an interval of approx. 1 to 2 seconds is typically required for this purpose. Angiography systems can generate projection recordings at such speeds without problem, and in this way trials relating to perfusion measurement in the heart have already been proposed, as disclosed in C. Michael Gibson and Albert Schömig: Coronary and Myocardial Angiography: Angiographic Assessment of Both Epicardial and Myocardial Perfusion. Circulation 109; pages 3096 to 3105, 2004. The projection methods have many disadvantages, however, in particular, an accurate assignment of an area in the projected image to the corresponding area of the three-dimensional anatomy is not possible.
There are also ideas for the measurement of perfusion by means of three-dimensional image recording in angiography systems (see DE 10 2006 030 811 A1, US 2007/0092055 A1 and Montes, P.; Lauritsch, G., “Analysis of time resolution in dynamic computed tomography for perfusion studies”, Nuclear Science Symposium Conference Record, 2004 EEEE, vol. 7, no., pages 4195 to 4199, Vol. 7, 16-22 Oct. 2004). For the 3D-recording, the C-arm of the angiography system has to rotate around the patient over an angular range of more than 180°, which restricts the time resolution to typically 4 to 5 seconds. The issue in these studies is therefore the problem of obtaining, despite the relatively poor time resolution, meaningful perfusion measurement values in the 3D recording by means of angiography systems.
However, the known methods are restricted to static, or in any case almost static, organs. In moving organs such as the heart, disruptions, referred to as artifacts, occur in the 3D images and therefore also in the perfusion images on account of the motion of the heart.
Methods also exist for mapping the heart in 3D by means of angiography systems (see DE 10 2004 048 209 B3, DE 10 2005 016 472 A1 and G. Lauritsch, J. Boese, L. Wigström, H. Kemeth, and R. Fahrig, “Towards Cardiac C-Arm Computed Tomography”, IEEE Transactions on Medical Imaging, vol. 25, pages 922 to 934, 2006); however, these require multiple 3D recordings simply for the ECG gating used for suppressing the motion of the heart. This adversely affects the temporal resolution so severely that perfusion measurements are not possible. ECG gating in this context means the use of a defined method with which by using the ECG signal in the 3D reconstruction a series of 3D images of a defined phase can be assigned as a result.
The fundamental problem of cardiac perfusion measurements is that to date by means of multiple rotational passes of the C-arm only either the cardiac phases can be taken into account by means of ECG gating or the temporal course of a contrast-agent bolus can be examined without ECG gating. Doing both simultaneously has previously not been possible.